Thermostatic switch



May 18, 1948. N. J. sMlTH THERMOSTATIC SWITCH v Filed Aug. 15, 1944 2Sheets-Sheet 1 nM z mb Q1 Q Qbv mmh. Sv v .N

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2 Sheets-Sheet 2 Uvafaaqys May 18, N 1 SMITH THERMOSTATIC SWITCH FiledAug. 15, 1944 ONM. ik im. ...l wm Il .94.3 1i l mh Iaaveiaoa.- y Normas@J'Smiu Patented May 18, 1948 UNITED STATES PATENT OFFICE THERMOSTATICSWITCH Norman James Smith, Medileid, Mass.

Application August 15, 1944, Serial No. 549,518

12 Claims. l

or contact members within the case have a relatively low rate of thermalexpansion relative to the case or shell. The longitudinal expansion orcontraction of the case is effective to produce relative movementbetween the contacts in a direction transverse to the axis of the case.In one type, the switch may be designed to open an electrical circuitupon reaching 'a predetermined temperature. The contacts are heldnormally closed under a compressive force sufficient to preventvibration which might result in defective operation. The relationbetween the longitudinal movement of the case and the lateral movementbetween the contacts constitutes the multiplication factor; for example,if the multiplication is 20 to l and the contacts are normally closedunder a force of two pounds, a longitudinal force of 40 pounds isrequired to open the contacts.

It is desirable to have a relatively high multiplication factor in orderthat the switch will operate within a relatively small thermaldifference and it would also be desirable to 4have a switch in whichsuch multiplication factor may be adjusted.

In a common type of thermostatic switch of this general character, thecontact members comprise a pair of bowed leaf springs. In such a switch,increasing the multiplication factor requires increasing the length ofthe case which may be commercially impracticable and such a switchcannot be designed for adjustment of the multiplication factor after ithas been constructed.

Thermostatic switches of this general type are designed to undershoot"or overshoot; that is, provision is made for relative lost motionbetween the contact members and the case; for example,

' in one type of switch, the contacts are biased to open position. andheld closed by compression in assembly, expansion of the case permitsopening of the contacts and thereafter the case is free to expand orcvershoot without further separa- (Cl. 20G-137) Lwith the desired degreeof pressure.

tion between the contacts. Similarly, in a switch of the type havingcontacts normally biased to closed position, the case is free tocontract or undershoot after the contacts have been closed Such lostmotion is usually provided between the contact carrying members and oneend of the case in which they are mounted.

It is an object of the present invention to provide a novel type ofthermostatic switch in which the contact carrying members are designedto operate on a new principle to permit variation in the multiplicationfactor without modifying the size or shape of the case and whereby themultiplication factor may be adjusted after the switch has beenmanufactured and before or after installation.

More specifically, it is the object of my invention to provide athermostatic switch in which one contact carrying element is fixed toone end of the case and the other contact carrying element is mounted atthe other end of the case, the two contact carrying elements beingconnected within the case by a transverse strut or post which is causedto deiiect or tilt to produce the relative lateral movement between theelectrical contacts.

It is further an object of my invention, to provide for adjustments ofthe transverse post which connects the contact carrying elements to varythe transverse separation between elements.

It is another object of my invention to provide a thermostatic switch inwhich one of the contact carrying elements is constructed withrelatively movable parts to permit the desired liberty of lost motionfor an "undershoot or overshoot type of thermostat.

It is still further an object of my invention to provide for holding thecontact carrying elements against rotation with respect to the case bymeans associated with the ends of the case rather than by a specialconfiguration of the case itself.

It is another object of my invention to provide a novel type ofadjustment for initial loading of the thermostatic switch by providingan adjusting screw having internal and external threads of differentialpitch, the screw having relatively coarse external threads andrelatively fine internal threads for setting a thermostat of thecompression overshoot type having contacts normally biased to open, andthe screw having relatively fine external threads and relatively coarseinterlnal threads for setting a thermostat of the tension overshoot typehaving contacts normally biased to closed position.

Additional objects an advantages of my improvements will be more readilyapparent from the following description lof preferred embodiments of myinvention as disclosed in the attached drawings, in which;

Fig. 1 is a longitudinal sectional view taken on the plane indicated I-Iin Fig. 4 through a thermostatic switch of the compression type in whichthe contacts are normally biased to open;

Fig. 2 is a. similar view showing a modified construction in which thereis provision for adjustment of the multiplication factor;

Fig. 3 is a longitudinal sectional view taken on the plane indicated3--3 in Figure 'l of a thermostatic switch of a type in which thecontacts are normally biased to closed position, but are opened onassembly and tendto close on expansion of the case;

Fig. 4 is an end view of the thermostatic switch shown in Fig. 1 lookingtowards the right hand end and showing the adjusting screw;

Fig. 5 is a cross-sectional view taken on the plane 5-5 in Fig. 1;

Fig. 6 is a cross-sectional view on the plane indicated 6-8 in Fig. 2;

Fig. 'I is an end view of the thermostatic switch shown in Fig. 3looking at the right hand thereof and illustrating the provision ofmeans for locking the adjusting screw;

Fig. 8 is a cross-sectional view on the plane indicated B--8 in Fig. 3;

Fig. 9 is a fragmentary longitudinal section at one end of a switch ofthe tension undershoot type in which the contacts are normally biased toclosed position;

Fig. 10 is a diagrammatic view showing the switch elements normallybiased to open position and the forces which cause the contacts to closein assembly; and

Fig. 11 is a diagrammatic view showing the switch elements normallybiased to closed position and the forces which act on the elements.

Referring to Fig. 1, there is shown a case or shell I0 having a bottomend I2 at the left hand end and a head I4 at the right hand end, thebottom end I2 has a screw threaded stud I8 mounting the turned up end I8of the strut 20 which constitutes one contact carrying member. The partI8 is fixed against rotation with respect to the stud I6. Above thestrut there is mounted a second strut or contact carrying member 22, theright hand end of which is received in the clevis 24 of thelongitudinally ad.- justable pin 26 which is threaded into the adlustingpin or bolt 28. The pin or bolt 28 is threaded into the head I4. The pin26 is held against rotation with respect to the case I0 by the provisionof a vertical pin 30 which passes through the clevis 24 and through anopening in the end of the strut 22. The pin 30 is free to slidelongitudinally but is held against rotation by being received in theclevis portion 32 of a stud 34 which is fixed to the head I4 by therivet 36.

The external threads 38 of the adjusting pin 28 are shown coarser thanthe internal threads 40 which engage the pin 28. It will be understood,therefore, that turning of the pin 28 to cause it to thread into thehead I4 and move in an inward direction will cause the pin 28 to threadinto the socket of the pin 28 but that due to the differential in pitchbetween the external and internal threads, the pin 28 will also moveinwardly with respect to the case I0.

The strut 22 has a pair of slots 42 and 44. A

4 bar or plate 48 is fastened to the strut 22 by the pins 48 and 80which are received in the slots 42 and 44 respectively. 'I'he pin 80also serves as a connection for the right hand end of the strut 20, theportion 82 of which is somewhat angularly disposed with respect to thestrut 22. At the left hand end of the case, electrical contact membersare mounted on the struts 20 and 22 as clearly shown in Fig. 5 in whicha clip 84 carrying a contact 88 is fastened to the strut 28 but isseparated therefrom by insulation 58 and a clip y8l) having a contact 82is similarly fastened to the left hand free end of the strut 22 beingseparated therefrom by insulation 84. An electrical cable 88 is attachedto theclip 54 and extends outwardly from the case through an opening 88in the head I4. A cable Iii is similarly attached to the clip andextends through an opening I2 in the head I4. The' struts 28 and 22, aswell as the bar 46 which forms a part of the upper strut 22 are composedof Invar or other ralloy having a relatively low rate of expansion. Theswitch shown in Fig. 1 is a compression type. During assembly, the strutor contact carrying member 22 is bent between the pin III and the pin 38in such a manner that it is resiliently biased to open position of thecontacts. Then by screwing in the adjusting pin 28, the contacts arecaused to V close by compression. This will be more clearly understoodby referring to Fig. 10 in which the strut 22, pin 50 and strut 20 arediagrammatically indicated. The arrows represent the compression forcesoppositely applied to the struts 20 and 22 which tend to close thecontacts. The screw 28 is adjusted so that the expansion of the case I0will permit the contacts to open at the desired temperature. screwingthe pin 28 inwardly with respect to the case will increase the settemperature. In Fig. 1 the switch-is close to the break point. Futherexpansion of the case will cause the contacts 58 and 62 to open. Afterthe contacts have opened, the case may further expand without furtherseparation of the contacts since the strut 22 is free to move withrespect to the pins 48 and 50. The slots 42 and 44 permit overshoot.

Fig. 9 shows a modified type of thermostatic switch very similar inconstruction to that of Fig. 1. It will be noted that the slot 44a instrut 22a is on the other side of the pin 80a and the fadjusting pin 28ahas fine exterior threads 38a and coarse interior threads 40a. In thistype, the strut 22a is bent during assembly to be resiliently biased toclose the contacts. Screwing in the adjusting pin 28a will cause the pin28a to thread into the pin 28a faster than the pin 28a moves into thecase. Therefore, the struts 20a and 22a will be placed under tension asindicated by the arrows in Fig. 11 and the resilient pressure betweenthe contacts will be relieved. Further expansion of the case will openthe contacts. As the case contracts, the contacts close and after theset point has been passed the case may further contract withoutincreasing the pressure or bending the strut 22a since the strut 22a isfree to move with respect to the pin 50a.

Fig. 11 also illustrates the effective lever arm I1 is the arm betweenthe pin 50a and the contact 82a. I2 is the vertical or lateral armformed by the pin 50a. I may be made quite small with respect to I1 sothe multiplication may be 20 to 1 or even as high as 40 to 1. Thus, thelongitudinal expansion of the case may be highly multiplied to producerapid separation of the contacts at the break point.

It may be very desirable to provide for adjustment of the multiplicationfactor to make the switch more or less sensitive or responsive to smallchanges in temperature. I have illustrated such. a switch in Fig. 2. Theconstruction in most respects is quite similar to Fig. 1 and the samereference characters are used so far as possible. A U-sh-aped bar Ilreplaces the bar Il. The strut 22 is pinned to the upper leg of the barIl by the pins 4I and Il while the strut 2l is pinned to the lower legof the bar 8l by the pin l2. The free ends of the U-shaped bar 8l areadjustably spaced by a screw threaded pin Il. The upper end of the pin uis accessible for adjustment by vremoving a cover applied to an openingin the case. The strut 22 has the same slots 42 and Il to receive thepins 4l and il while in addition a slot Il is provided for the screw pinIl. The operation is the same as in Fig. 1. The switch may be made atension undershoot type as well as the compression overshoot Aas shown.During assembly or after being installed. the multiplication factor maybe adjusted by turning the screw Il.

It may be desirable to have the contacts open at normal temperature butarranged to close on an increase in temperature. Buch a switch is shownin Fig. 3. The construction is in many I' respects similar to Fig. 1.The pin or'stud i0 at the bottom end ofthe case mounts' a strut ll whichhas an extension t2 to which is attached a contact u, facing downwardly.The other strut l is similar to the strut I! in Fig. 1 and carries acontact Il facing upwardly to cooperate with contact Il. The strut isfastened to a bar IM by pins |02 and IM. The pin III serves to hold oneend of the strut lll. It will be understood that the strut It is bentduring assembly to resiliently press the contacts I4 and il together.but screwing in the adjusting pin II will place the struts undercompression and open the contacts. Expansion of the case will allow thecontacts to close as the compression or initial loading is relieved.

Fig. 3 also shows an arrangement which may be used for locking theadjusting pin 2l. A pair of plates I0! and ill are threaded on the pin2l. The plates I" and Ill are squeezed together to tighten and bind onthe screw 2l by tightening the screws H0 which pass freely through theouter plate i but thread into the inner plate I. The inner ends of thescrews lll are received in the holes il! bored in the head il.

In all forms of the thermostatic switch one of the struts or contactcarrying elements forms in effect an L-shaped lever since the pin towhich the other strut or contact element is connected is rigid with thefirst strut in transmitting movement by tension or compression actingthrough the second strut. The spring rating is determined by thecross-section of the first strut between the lever arm pin and thesupported end of the first strut and to a minor extent by the springrating of the second strut. It should be noted that the contact clipsare fastened on flat portions of the struts and do not effect the springrating.

I claim:

1. In a thermostatic switch, a support. a pair of struts mounted on saidsupport, cooperating electrical contacts on -said struts, said supporthaving a thermal expansion rate greater than said struts, one of saidstruts having a relatively short transverse lever arm associated withsaid 6 Y v strut whereby said strut and said lever arm forms a rigidL-shaped lever strut, said L-shaped lever strut being resilientlymounted with respect to said support. and the 4other of said strutsconstituting a resilient leaf spring member fixed at one end to saidsupport and at the other end to the short arm of said L-shaped leverstrut whereby diiferential expansion of said support with respect tosaid struts will cause relative movement between said contacts. t'

2. In a thermostatic switch, a casing having a bottom end and a head, aleaf spring member fixed to the bottom end of said casing and ex tendingtowards the head thereof. a contact carried by said leaf spring membernear the fixed end thereof. a lever member having a long arm and arelatively short transverse arm associated therewith. said leaf springmember being fixed to the short arm of said lever member. a contactcarried by the long arm of said lever member and adapted to engage thefirst mentioned contact. said lever member having a rela'tlvely shortresilient extension from the juncture between said lever arms formounting said lever on the head of said casing, said casing having athermal expansion rate greater than said leaf spring and said lever,said lever being initially biased by bending said resilient extensiontowards separation of said contacts, means for longitudinally adjustingthe mounting of said lever with respect to said head to cause saidcontacts to close, whereby said contacts will open at a predeterminedtemperature as the casing expands. l 3. In a thermostatic switch. acasing having a bottom end and a head, a leaf spring member fixed to thebottom end of said casing and extending towards the head thereof, acontact carried by said leaf spring member near the fixed end thereof, alever member having a long arm and a relatively short transverse armassociated therewith, said leaf spring member being fixed to the shortarm of said lever member, a contact carried by the long arm oi' saidlever member and adapted to engage the first mentioned contact, saidlever member having a relatively short resilient extension from thejuncture between said lever arms for mounting said lever on the head ofsaid casing, said casing having a thermal expansion rate greater thansaid leaf spring and said lever,v said lever being initially ybiased toclose said contact and means for longitudinally adjusting the mountingof said lever with respect to said head to adjust the pressure betweensaid contacts whereby said .contacts will open at a predeterminedtemperature as the casing exbands.

4. In a thermostatic switch, a casing. a contact carrying member mountedin said casing and supported at one end thereof, a second contactcarrying member mounted in said casing and supported at the opposite endthereof and means for producing relative lateral movement between thecontacts oiv the contact carrying members by relative longitudinalmovement between the supported ends of said members comprising asubstantially rigid lateral lever arm associated with one of saidmembers and a connection between the other member 'and said leverarmwhereby oppositely directed f o r c e s acting through said members atspaced points on said lever arm caused by differential thermal expansionof said casing with respect to said members conttsrol the lateralmovement between said contac 5. In a thermostatic switch, a tubular casehaving a bottom end and a head, a rst strut fixed to the bottom end ofsaid case, a second strut mounted on the head oi' said case, a pair ofcontacts on said struts near the bottom end of said case, means xingsaid first strut to said second strut near the head of said case andforming in eiect a. relatively short lever arm between said struts. oneof said struts having a slot to receive said means whereby oppositelydirected forces acting at spaced points through said struts on saidmeans will produce relative lateral movement between said contacts up toa predetermined point after which relative longitudinal movement betweensaid struts may take place as said means is free to move with respect tosaid slot.

6. In a thermostatic switch, a tubular case having a bottom end and ahead, a rst strut ilxed to the bottom end of said case, a second strutmounted on the head of said case, a pair of contacts on said struts nearthe bottom end of the case, means for fixing said rst strut to one sideof said second strut near the head of said case whereby said means formsin eiect a relatively short lever arm between said struts and relativelongitudinal movement between the ends of said case will produceoppositely directed forces acting on said lever arm to cause relativelateral movement between said contacts at a multiplied rate.

7'. In a thermostatic switch, a tubular case, a pair of contact carryingstruts fixed respectively to the opposite ends of said case, 'means forcausing relative longitudinal movement between the ends ci' said case toproduce relative lateral movement between said contacts at a multipliedrate and means for adjusting the multiplied rate to vary the sensitivityof the thermostatic switch.

8. In a thermostatic switch, a tubular case, a pair of contact carryingstruts fixed respectively to the opposite ends of said case, means forcausing relative longitudinal movement between the ends of said case toproduce relative lateral movement between said contacts at a multipliedrate and means accessible from the exterior o! the case for adjustingthe multiplied rate to vary the sensitivity of the thermostatic switch.

9. In a thermostatic switch, a tubular case, a pair of contact carryingstruts xed respectively to the opposite ends of said case, means forcausing relative longitudinal movement between the ends of said case toproduce relative lateral movement between said contacts at a multipliedrate and a screw threaded connection between said struts adjustable tochange the multiplied rate to vary the sensitivity of the thermostaticswitch.

10. In a thermostatic switch, a tubular casing having a bottom end and ahead, a first strut fixed to the bottom end of said casing, an adjustingscrew threaded into said head a second screw threaded into saidadjusting screw, a second strut fixed to said second screw, a pair oi'cooperating contacts carried by said struts near the bottom end of saidcasing, means for fixing said first strut to said second strut andforming in eiect a short lever arm and means mounted on said head forholding said second screw against rotation while permitting relativelongitudinal movement with respect to said head.

11. In a thermostatic switch, a casing, 9. pair of contact carryingelements mounted in said casing, means for connecting one of saidelements to one end of said casing, means for connecting the other ofsaid elements to the opposite end of said casing, a connection betweensaid elements intermediate the ends of said casing and means at saidconnection for permitting limited longitudinal movement between saidelements.

12. In a thermostatic switch, a casing, a pair of contact elements insaid casing responsive to longitudinal expansion of .said casing byrelative lateral movement between the contacts of said elements, one ofsaid elements being composed of two parts. and means for fastening saidparts together to permit limited longitudinal movement between the partsof said element.

NORMAN JAMES SMITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

